We are implementing Microsoft Exchange on a EMC DMX3500 DASD Subsystem that has 146GB and 300GBs. Talked to Gartner Group Consultant Bob Passmore and he is strongly recommending RAID 1: his justification is based on the fact that RAID 1 is double the number of disk drives; therefore you cut what is called QUEUE DEPTH of the data path in half which will significantly help performance. Exchange data is small blocks of data; short I/O burst and RAID 1 will work a lot faster. With RAID 5 you are spreading the writes across multiple drives; however, it is to fewer drives and the QUEUE DEPTH is significantly increased even in normal I/O activity. You asked what Queue depth is: it is the number of I/O operations that can be run in parallel on a device. It is usually possible to set a limit on the queue depth on the subsystem device driver (SDD) paths (or equivalent) or the host bus adapter (HBA). Also general recommendations are to utilize Raid 1 for transaction log files SMTP queues and MTA queues. After Exchange Server's databases and transaction logs, the resources that consume the highest number of disk I/Os are queues. Exchange Server uses two different queues: the MTA queue and the SMTP queue. MTA queues are used as a temporary message repository for messages received from Exchange 5.5 servers, or for messages that arrive via an X.400 connection. MTA queues are also used to temporarily store messages that arrive while a mailbox is being moved. SMTP queues handle inbound and outbound SMTP messages. Whether or not you decide to group the SMTP and MTA queues together, they need to be placed on a dedicated partition. Microsoft recommends a SAN-based RAID 1 volume. Some administrators have been known to cut corners and not use a dedicated volume for the SMTP and MTA queues. If you decide that you don't want to use a dedicated volume for Exchange Server's queues, then it is extremely important that you don't place the queues on the same volume as the Exchange databases or transaction logs. And finally; the storage vendor that we are utilizing toady EMC is recommending RAID1 for Microsoft Exchange data. Would you agree with the above statements. My management want to place Exchange on RAID 5.